I can't hear any sound!

Did OSS load at all? Run the command to examine loaded modules specific to your OS (lsmod, kldstat, etc.) to find out.

Does osstest work?

Are the outputs muted in the mixer?

Do the device nodes (/dev/dsp, /dev/oss directory, etc.) exist (osstest should complain if they don't)? If not, restarting OSS would probably create them. However, the following two commands should create them without need to restart:

sudo ossdevlinks -r -v

sudo ossdetect -d -v

Is the default output (the one linked to /dev/dsp) the one connected / outputting sound in osstest? If not, see here how to change that.

HDAudio: Are the jacks detected by OSS as output, actually the jacks connected to the speaker?

Ich: Some computers have an inverted external amplifier settings, so setting ac97_amplifier to 0 in $OSSLIBDIR/conf/osscore.conf would help. Gateway notebooks (Gateway 4542GP, 4028GZ, 7326GZ) in particular often have this bug.

$OSSLIBDIR is typically /usr/lib/oss, and can be determined exactly by the contents of /etc/oss.conf.

Is this an hardware issue?

Are the speakers muted?

Is the soundcard connected correctly to the speakers?

Do other drivers available for your OS (e.g. ALSA for Linux, FreeBSD native) work?

I hear noises!

Many soundcards' hardware requires output mixers be set to less than maximum (even down to 60% with a few cards).

Set vmix0-src to an higher setting using a mixer program like ossxmix.

Is the cable from the soundcard to the speakers connected correctly? Could it be too long?

Build and use OSS using the source from the public hg repository, perhaps a newer version will work better.

I can't get multiple sound clients to play on the same device!

OSSv4.0 for the FreeBSD platform doesn't support multiple clients to same device node on /dev/dsp device node (OSSv4.0 does support this on other platforms like Linux). It instead splits the mixing to separate devices: /dev/dsp1, /dev/dsp2, etc. Either set programs to use separate devices, or use a sound server like aRts, esd, etc., or upgrade to v4.1 which supports multiple clients on FreeBSD 7.1 and up.

Is vmix loaded and attached to the device? (Check if 'ossinfo -v3' shows more than one engine for the output device).

In OSS 4.0, (Doesn't apply to build 1016:) If vmix is not attached, make sure vmix1_masterdev in $OSSLIBDIR/conf/vmix.conf is set to the output device's device index (this can be determined via 'ossinfo -a'). ($OSSLIBDIR is typically /usr/lib/oss).

In OSS 4.1, 'vmixctl' command is used instead of vmix.conf (requires root permissions).

Are the vmix controls in ossxmix unmuted?

I can't get multichannel/5.1 output to play!

Some configurations require more than one cable connected to the speaker set. Make sure that as many cables as required are connected.

Some devices have the multich output at a different device node than the regular one, use /dev/dsp_multich rather than /dev/dsp as /dev/dsp_multich is always linked to the correct device. In the case of Dolby digital/AC3, /dev/dsp_ac3 is the best device instead of /dev/dsp_multich. It is possible that the node /dev/dsp_multich is symlinked to doesn't have vmix attached, so multiple clients won't play. See the tip above for how to fix this.

Some devices require changing settings in the mixer (e.g. by 'ossmix' or 'ossxmix') to work.

In OSS 4.0, (Doesn't apply to build 1016:) Set vmix1_multich=1 in $OSSLIBDIR/conf/vmix.conf ($OSSLIBDIR is typically /usr/lib/oss).

In 4.1, set vmix0-channels to "Multich" in the mixer.*sblive/audigy devices may require use of the sblive_digital_din (or audigy_digital_din) option in the device configuration file - see driver manpage.